Drying of concrete as a nonlinear diffusion problem

Numerous experimental data on drying of concrete and cement paste are subjected to computer analysis. It is found that for a satisfactory fit of the data the diffusion coefficient must be considered to be a function of pore relative humidity (or specific water content), which makes the diffusion problem of drying nonlinear. The diffusion coefficient is shown to decrease sharply (about 20-times) when passing from 0.9 to 0.6 pore humidity, while below 0.6 it appears to be approximately constant. Improvement over the linear theory used in the past is very substantial and indicates that a realistic prediction of drying is possible.